The engine valve cover gasket is a rubber seal that fits between the engine cylinder head and the valve cover to prevent fluids from leaking from the valve cover while the valve train is running and lubricated. This seal generally should be replaced if the valve cover is removed for maintenance to make sure a proper seal is made between the two surfaces. Due to high heat and chemical exposure, the valve cover gasket can become brittle and lose the ability to seal on the cylinder head, causing oil leaks around the circumference of the engine, and also in the valley containing the spark plugs.